When multi-level converters are used as STATic (VAR) COMpensators (STATCOMs), the arm capacitor voltages diverge and controlled zero sequence reference voltage injection(s) at the fundamental frequency is required to keep them balanced. This is a particularly serious issue when the converter currents and/or voltages are imbalanced.
There is lacking control solutions that offer a unified treatment of star (with and without a neutral conductor) and delta topologies in all operational regimes including the most general situations when the converter currents and voltages are imbalanced. Existing feedforward calculations of the zero sequence injection(s)s also do not consider the effect of a voltage drop on the zero sequence inductance.